Running into Typescript state type mismatch error

It seems to me that I have all the types correct, however am I missing a different kind of Reducer type?

IinitialAssetsState' is not assignable to type 'Reducer'

The full error:

Type '(state: { assets: never[]; portfolio: never[]; loading: boolean; } | undefined, action: any) => IinitialAssetsState' is not assignable to type 'Reducer'.

Types of parameters 'state' and 'state' are incompatible.

Type 'IinitialAssetsState | undefined' is not assignable to type '{ assets: never[]; portfolio: never[]; loading: boolean; } | undefined'.

Type 'IinitialAssetsState' is not assignable to type '{ assets: never[]; portfolio: never[]; loading: boolean; }'.

Types of property 'assets' are incompatible.

Type 'IAsset[]' is not assignable to type 'never[]'.

Type 'IAsset' is not assignable to type 'never'.

My store.ts file

import { applyMiddleware, createStore, combineReducers } from 'redux'
import { composeWithDevTools } from 'redux-devtools-extension'
import thunkMiddleware from 'redux-thunk'

import { IinitialState } from './shared/types'
import { AssetsReducer } from './reducers/assets'
import { BoardReducer } from './reducers/board'

const rootReducer = combineReducers({
  AssetsReducer,
  BoardReducer
});

export const defaultInitialState = {
  AssetsReducer: { assets: [], loading: false, portfolio: [] },
  BoardReducer: { overlay: false },
}

export function initializeStore(initialState: IinitialState = defaultInitialState) {
  return createStore(
    rootReducer,
    initialState,
    composeWithDevTools(applyMiddleware(thunkMiddleware))
  )
}

AssetsReducer

import { Actions } from '../actions/assets'
import { IinitialAssetsState } from '../shared/types'

const defaultAssetsState = { assets: [], portfolio: [], loading: false };

export const AssetsReducer = (state = defaultAssetsState, action: any): IinitialAssetsState => {
  switch (action.type) {
    case Actions.GET_ALL_ASSETS: {
      const { assets } = action;
      return {
        ...state,
        assets,
        loading: false
      };
    }

    default:
      return state;
  }
};

BoardReducer

import { Actions } from '../actions/board'
import { IinitalBoardState } from '../shared/types'

const defaultBoardState = { overlay: false };

export const BoardReducer = (state = defaultBoardState, action: any): IinitalBoardState => {
  switch (action.type) {
    case Actions.SET_OVERLAY_STATE: {
      const { overlay } = action;
      return {
        overlay
      };
    }

    default:
      return state;
  }
};

My types file

export interface IAsset {
  position: number;
  marketCap: number;
  name: string;
  percentage: number;
  price: number;
  currency: string;
  value: number;
}

export interface IinitialAssetsState {
  assets: IAsset[];
  portfolio: IAsset[];
  loading: boolean;
}

export interface IinitalBoardState {
  overlay: boolean;
}

export interface IinitialState {
  AssetsReducer: IinitialAssetsState;
  BoardReducer: IinitalBoardState;
}

What I've tried

I created a type for the action to remove the use of any, but I still run into the same Typescript error:

interface IAssetsAction {
  type: string;
  assets: IAsset[];
}

export const AssetsReducer = (state = defaultAssetsState, action: IAssetsAction): IinitialAssetsState => {
  console.log('action', action);
  switch (action.type) {
    case Actions.GET_ALL_ASSETS: {
      const { assets } = action;
      return {
        ...state,
        assets,
        loading: false
      };
    }

I believe this might be the problem in store.ts:

export const defaultInitialState = {
  AssetsReducer: { assets: [], loading: false, portfolio: [] },
  BoardReducer: { overlay: false },
}

Here defaultInitialState.assets is of type never[].

You need set the type for defaultInitialState

export const defaultInitialState : IinitialState  = {
  AssetsReducer: { assets: [], loading: false, portfolio: [] },
  BoardReducer: { overlay: false },
}

Edit: Also in AssetsReducer and BoardReducer

const defaultBoardState : IinitalBoardState = { overlay: false };